1. Field of the Invention
The invention relates to a vacuum pump, in particular to a turbomolecular pump or a side channel pump, having a working space, a bearing space, a dividing wall arranged between the working space and the bearing space and a rotor shaft extending through the dividing wall.
2. Description of the Prior Art
Vacuum pumps are used in different technical processes to provide a vacuum required for the respective process. A vacuum pump typically comprises a working space, a bearing space, a dividing wall arranged between the working space and the bearing space and a rotor shaft. A pump structure of the vacuum pump is arranged in the working space, the pump structure conveying the process gas present in the working space from the inlet to the outlet of the vacuum pump and thereby pumping said process gas. A bearing for supporting the rotor shaft and, optionally, a drive for the rotor shaft are e.g. arranged in the bearing space. The rotor shaft extends through the dividing wall while forming a gap. In this respect, a section of the rotor shaft which carries the part of the pump structure at the rotor side extends into the working space and another section of the rotor shaft which is e.g. connected to the bearing extends into the bearing space.
A problem with known vacuum pumps is represented by corrosive gases and other damaging gases which are contained in the conveyed process gas and move through the gap formed between the rotor shaft and the dividing wall from the working space into the bearing space. These gases attack the bearings, operating media and further components present in the bearing space, which can result in damage and in a premature failure of the pump.
To block the bearing space from the working space, i.e. to prevent an unwanted gas exchange between the working space and the bearing space, a labyrinth seal can be provided between the rotor shaft and the dividing wall. The labyrinth seal can comprise a plurality of axial recesses of a rotor disk which follow one another in the radial direction and which mesh with corresponding projections of the surrounding dividing wall so that a long and narrow gap is formed between the rotor shaft and the dividing wall which effects a sealing. In principle, the labyrinth seal can also comprise a plurality of radial recesses of the rotor shaft which follow one another in the axial direction and which form a long and narrow sealing gap with the dividing wall.
A disadvantage of a vacuum pump having such a labyrinth seal is that very narrow gaps are required for a high sealing effect and said narrow gaps can only be achieved with difficulty due to the thermal expansions which occur in the operation of the vacuum pump and due to the expansions based on the centrifugal forces which occur at high rotational speeds. In addition, the provision of a vacuum pump having such a labyrinth seal is associated with a high additional manufacturing effort. The recesses in the rotor disk can furthermore result in the occurrence of unfavorable mechanical strains in the rotor during the pump operation which impair the service life and the operating safety of the vacuum pump. The labyrinth seal additionally produces a substantial increase in the axial construction height and in the power requirement of the vacuum pump due to the gas friction which occurs in the narrow gaps.
It is therefore an object of the invention to provide a vacuum pump which overcomes the above-described disadvantages, that is a vacuum pump in which a damaging exchange of gas between the working space and the bearing space is avoided, the vacuum pump at the same time being able to be manufactured with a small effort, being able to be realized in a small construction space and having a small power requirement and a high service life.